1. Field of The Invention
This invention relates to encoding and decoding methods for use in a facsimile.
2. Description of The Related Art
In case of compressing raw data (namely, Non-Coded Format data (hereunder abbreviated as NC data)), which is read by a scanner, in a conventional facsimile, the NC data is converted or encoded en bloc into Modified Huffman (hereunder abbreviated as MH) data or Modified Read (hereunder abbreviated as MR) data. Further, in case of expanding MH data or MR data received by a conventional facsimile, NC data is decoded en bloc from the MH or MR data. Such an encoding or decoding operation is performed by using a large scale integrated circuit (LSI) dedicated to an encoding or decoding. Alternatively, such an encoding or decoding is effected by a general purpose arithmetic and logic unit by using a central processing unit (CPU) of the conventional facsimile.
Further, image information corresponding to each line of a draft, which is read by the scanner of the conventional facsimile, is written to a memory as a bit string, of which each bit corresponds to a pixel. In case of performing a conversion of resolution of such image information (for example, condensing a draft image, of which the size is B4, into a converted image, of which the size is A4), for example, a thinning of bits of a bit string corresponding to each line is performed at predetermined thinning intervals (for instance, every sixth bit, every seventh bit, every seventh bit and every sixth bit corresponding to first, second, third and fourth lines, respectively).
When using LSI dedicated to an encoding or decoding (hereunder sometimes referred to as an encoding/decoding LSI), a control operation of an LSI fitted on the outer surface of such an encoding/decoding LSI should be performed in addition to a providing of the encoding/decoding LSI for effecting an encoding or decoding operation. Further, when accepting data, means for performing an interruption/Direct Memory Access (DMA) operation/a polling operation are required for accepting the data. This results in increase in burden to the CPU of the conventional facsimile. In contrast, in case of employing a general purpose arithmetic and logic unit, a compressing/expanding of data can be effected only when the burden to the CPU is small.
Moreover, as described above, a conversion of resolution is attended with operations such as a thinning of bits of a bit string corresponding to each line of an image. This complicates a processing to be performed in connection with the conversion of resolution. For example, in case where the conventional facsimile is provided with a memory for storing a received message, the conversion of resolution should be effected after MR code or data is decoded or coded back to NC data.
The present invention is accomplished to resolve the above described problems of the conventional facsimile.
It is, therefore, an object of the present invention to provide decoding and encoding methods for performing conversions among NC, MH and MR data by using a cumulative run-length as what is called an intermediate code without using hardware for an encoding and decoding.